Agriculture Reference
In-Depth Information
Fig. 4.3
Relationship between
leaf longevity and specific leaf
area.
Lines
and
curves
in the
panels follow from (4.18)
in the text. When
k
= 0, the
relationships are linear and when
k
= 0.08, they are curvilinear;
the instantaneous potential
translocation rate
E
and lifetime
transportation
R
are parameters.
(From Westoby et al. 2000)
a
k = 0.00 mo
-1
100
10
1
b
k = 0.08 mo
-1
100
10
1
1 10
Specific leaf area (mm
2
mg
-1
) [log scale]
100
and SLA (the inverse of LMA) when other factors are held constant (Fig.
4.3
).
When
k
= 0, the logarithm of leaf longevity decreases linearly with log (SLA), but
if
k
takes a positive value, then the relationships become curvilinear and convex to
the bottom. The analysis makes it clear that because photosynthetic rate and thus
translocation rate change with time, it is necessary to incorporate these changes in
modeling of leaf longevity.
Leaf Longevity and Leaf Turnover in Plant Canopies
The preceding models have focused on longevity as a leaf-level trait and invoked
canopy-level influences in only a generalized way. There is another literature tracing
back to a seminal paper by Monsi and Saeki (1953) on the characteristics of plant
canopies that deals with leaf longevity secondarily through the rate of leaf turnover
in the canopy. When a plant canopy is in steady state, leaf longevity is the inverse
of leaf turnover in the canopy. The pioneering work by Monsi and Saeki (1953)
focused on the concept of an optimum leaf area per unit land area, an optimal leaf
area index (LAI). They used the then-novel method of stratified clipping to assess
the vertical distribution of leaf area in various plant communities. These data on
canopy structure stimulated development of theory predicting the aggregate char-
acteristics of leaves in different canopy strata. Because of the close correlation
between foliar nitrogen and photosynthetic capacity and the recognition that nitrogen
